The more frequent mass jellyfish occurrences had negative consequences on the zooplankton and juvenile fish in all seas of the world as well as for total fisheries, industry and tourism. They are several possible causes of these phenomena and they are mostly indirectly associated with human activities. Among them, climate change and ocean temperature rise have a particularly important role. In this study we will show the results of long-term data gathering (1995-2017) on the planktonic scyphozoans and ctenophore occurrence and abundance along the eastern Adriatic coast. Most of the data were obtained on the basis of reports organized through the actions of "Citizen Science", but also by scientists and other employees of the Adriatic Institutes. The monitoring area is divided into three regions according to ecological features: the northern, middle and southern part of the Adriatic. Collected data are mostly semi-quantitative and relate to each species individually, and includes a wide range of information covering different temporal and spatial scales. Detailed phenology and population densities will be presented for the constantly present scyphozoans species: Rhizostoma pulmo, Cotylorhiza tuberculata, Chrysaora hysoscella, Pelagia noctiluca, Aurelia spp., but also for less common species. The composition, phenology and abundance of the eastern Adriatic comb jelly will be shown for the first time with special reference to the mass phenomenon of the Mnemiopsis leidyi in the northern Adriatic. Changes in the phenology and abundance of scyphozoans and ctenophores compared to historical studies can be attributed to the global rise of sea temperature for the entire eastern Adriatic coast. The results confirm the global findings that characterized the mass occurrences of gelatinous zooplankton in waters with more pronounced anthropogenic influence.